Semi-Empirical Modeling of Fuselage-Rotor Interference for Comprehensive Codes: Influence of Side-Slip Angle

Abstract

A semi-empirical and physics-based analytical formulation of the induced velocities generated by the fuselage shell of the Bo105 wind tunnel model in the volume around the rotor is derived from velocity data computed by a panel code. The reduced-order analytical model is several orders of magnitude faster than the panel code and thus is predestinated for use in comprehensive rotor codes. Angle of attacks investigated include vertical descent, shallow descent, level flight and climb to vertical ascent. Side-slip angles range from forward to quartering flight. The analytical induced velocity model can be directly used to account for the inflow at the blade elements and also allows for analytical or numerical integration of rotor wake convection to compute the associated displacements of rotor blade tip vortices travelling downstream within this velocity field. This model will be used to replace a fully panelized fuselage (and thus significantly reduce the computational effort) throughout a simulation with an aeromechanics code to account for the influence of the fuselage (e.g., in a design stage). The usage within an aerodynamics code (e.g., a panel code) reduces the panelization to the rotor blades only, leaving the computation of the fuselage-induced velocities to the model. The focus of this paper is the analytical evaluation of fuselage–rotor interference in side-slip angles on rotor trim controls, using blade element momentum theory. The results are compared to the influence of thrust-induced inflow gradients on rotor trim.